Backbone resonance assignments for G protein αi3 subunit in the GTP-bound state

Guanine-nucleotide binding proteins (G proteins) act as molecular switches in signaling pathways, by coupling the activation of G protein-coupled receptors (GPCRs) at the cell surface to intracellular responses. In the resting state, G protein forms a heterotrimer, consisting of GDP-bound form of the G protein alpha subunit (G alpha(GDP)) and G protein beta gamma subunit (G beta gamma). Ligand binding to GPCRs promotes the GDP-GTP exchange on G alpha, leading to the dissociation of the GTP-bound form of G alpha (G alpha(GTP)) and G beta gamma. Then, G alpha(GTP) and G beta gamma bind to their downstream effector enzymes or ion channels and regulate their activities, leading to a variety of cellular responses. Finally, G alpha hydrolyzes the bound GTP to GDP and returns to the resting state by re-associating with G beta gamma. G proteins are classified with four major families based on the amino acid sequences of G alpha: i/o, s, q/11, and 12/13. Each family transduces the signaling from different GPCRs to the specific effectors. Here, we established the backbone resonance assignments of human G alpha(i3), a member of the i/o family, with a molecular weight of 41 K in complex with a GTP analogue, GTP gamma S.